Modern cameras actually not that different from the cameras of a century ago. Every camera consists of three vital organs:
Back with the photographic material (what we're shooting on), body, lens.
Any camera consists of these three parts.
The exposition is fundamentally influenced by three parameters: the amount of light passing through the optical scheme - which is regulated by a diaphragm. How long photomaterial is subjected to expose - is governed by the shutter speed. And the film speed of the photomaterial.
Also on the final image have affects focus, but it does not affect the exposure.
In a camera, demonstrated above, all the parts are separable and interchangeable. Inside the back is a film or digital matrix in the process of shooting with this camera, the film can be changed, as well as you can shoot on a digital matrix. In the body of this camera is a mirror and a viewfinder shaft, as well as mechanical shutter control. The shutter in this system is located in the lens.
There are also compact 35mm SLR cameras, where the back and body united in a common housing. In these cameras you can not change a film during the shooting, and you can not shoot at a variety photomaterials. While most modern cameras of this type is digital. Also in the 35mm SLR cameras the shutter is located in the body and basically is focal-plane shutter. In this system only lens are replaceable.
In a amateur cameras all its systems are located in the same body and you can not replace or use other.
There are large-format cameras also called view-cameras. In these cameras role of the body serves bellows. This allows the front and rear bars (plane of the lens mount and the back mount) are movable relative to each other. It is used to adjust the perspective and focus.